1. Field of the Invention
The present invention generally relates to semiconductor-processing by ultraviolet (UV) radiation and cleaning of a ultraviolet (UV) radiation chamber for semiconductor-processing, particularly cleaning of an optical transmitted window provided in a UV irradiation chamber.
2. Description of the Related Art
Traditionally, UV processing apparatuses have been used in general in the property modification of various processing targets by means of UV light as well as in the production of substances that utilize photochemical reaction. With the trend for higher integration of devices in recent years, wiring designs are becoming finer and multi-layer wiring structures are being adopted, which in turn is making it necessary to reduce inter-layer volumes in devices to achieve higher processing speeds and lower power consumptions. Low-k (low dielectric constant film) materials are used to reduce inter-layer volumes in devices. As the dielectric constant drops, however, mechanical strength (elastic modulus, or EM) also drops and the low-k material thus becomes less resistant to stress received in the subsequent processes such as CMP, wire bonding and packaging. One method to address the aforementioned problem is to cure the low-k material through UV irradiation to improve its mechanical strength (refer to U.S. Pat. Nos. 6,759,098 and 6,296,909 for examples). UV irradiation causes the low-k material to contract and harden, resulting in an improvement of mechanical strength by 50 to 200%.
Another requirement resulting from the recent trend of high-integration devices is to obtain various thin films using thermal CVD or PECVD in a condition free from heat or plasma damage. To meet this requirement, photo-CVD that utilizes photochemical reaction has been studied.
However, irradiating optical energy onto the processing target or reaction space by any of the aforementioned methods requires the UV lamp to be separated from the reaction space because: (1) the pressure in the reaction space must be controlled along with the ambient gas, (2) the generated gas can contaminate the UV lamp, and (3) the generated gas must be discharged safely. As a division plate used for this purpose, normally optical transmitted window made of synthetic quartz, a material that transmits optical energy, has been traditionally employed.